1. Field of the Invention
The present invention generally relates to methods for manufacturing semiconductor devices and split-molds used therein, and more particularly to a method for manufacturing Chip Size Package (CSP) type semiconductor devices and a split-mold used therein.
In recent years, with increasing demand for miniaturized electric equipment, a semiconductor device installed therein has also been required to have a smaller size (high density). In order to support this situation, the semiconductor device is made to have a size approximately the same as that of a semiconductor chip contained therein. Such a semiconductor device is referred to as the CSP type semiconductor device. The CSP type semiconductor device has a chip thereof encapsulated in resin so as to improve reliability while maintaining miniaturization.
The CSP type semiconductor device, on the other hand, needs to be manufactured with high productivity. Therefore it is very useful to improve productivity of a process for encapsulating the chip with the resin.
2. Description of the Related Art
FIGS. 1 through 4 show a conventional method for manufacturing such a CSP type semiconductor device and a conventional split-mold used in the method. The method includes a step for forming a resin layer serving to encapsulate a substrate on which a plurality of semiconductor chips are formed.
Specifically, FIG. 1 is a diagram schematically showing a split-mold 20 used for manufacturing the CSP type semiconductor device. As shown in this diagram, the split-mold 20 mainly includes a male mold 21 and a female mold 22 both of which are provided with heaters (not shown) serving to heat and melt encapsulating resin 35 that will be described later.
The male mold 21 is configured to be able to be moved up and down as shown by arrows Z1 and Z2 in FIG. 1. Further, the male mold 21 has a pressing surface 21a formed at the bottom thereof serving to apply a pressure to the encapsulating resin 35. The pressing surface 21a is a flatted surface.
The female mold 22, on the other hand, is configured to have a first female mold 23 that is shaped like a cylinder and a second female mold 24 that has an annular shape. The first female mold 23 is formed corresponding to and slightly larger than a substrate 16 in dimension. The substrate 16 is mounted on a pressing surface 25 of the first female mold 23. The second female mold 24 has a cavity surface 26 formed on an inner wall thereof, serving to provide space to accommodate the remainder of the encapsulating resin 35.
The second female mold 24 is configured to be approximately annular so as to surround the first female mold 23. Further, the second female mold 24 is able to be moved up and down with respect to the first female mold 23 along the arrows Z1 and Z2, that is, to approach to or separate from the pressing surface 21a of the male mold 21.
FIG. 1 also shows a state immediately prior to the beginning of a process for forming a resin layer. As shown in this diagram, in this state, the second female mold 24 is moved up with respect to the first female mold 23 in the direction Z2. By this movement, a space is formed between the first and second female molds 23, 24, serving to accommodate the substrate 16 on which a plurality of bumps (protruding electrodes) 12 are formed. In addition, in this state, the bumps 12 formed on the substrate 16 face toward the male mold 21.
Further, a mold release sheet 30 is attached to the pressing surface 21a, and the encapsulating resin 35 is placed on the bumps 12 of the substrate 16.
FIG. 2 is a top view, as seen from the male mold 21, showing a state of the encapsulating resin 35 being placed on the bumps 12. In this diagram, reference numeral 11 denotes a plurality of semiconductor chips before the substrate 16 is diced.
As previously described, when the process of mounting the substrate 16 and the process of providing the encapsulating resin 35 are completed, a process of forming a resin layer is performed. In the resin-layer forming process, the male mold 21 including the heater is moved down in the direction Z1 while heating the encapsulating resin 35, until the encapsulating resin 35 begins to melt.
The male mold 21 is thus moved down in the direction Z1 to contact the second female mold 24. Since the male mold 21 is provided with the mold release sheet 30 on the bottom thereof as previously described, when the male mold 21 contacts the second female mold 24, as shown in FIG. 3, the mold release sheet 30 is clamped therebetween. Further, the male mold 21 is provided with a sucking groove 29, which is connected to a vacuum source (not shown) and serves to suck a peripheral portion of the mold release sheet 30 so as to apply tension thereto. Such a configuration aims to prevent the mold release sheet 30 from generating wrinkles thereon. At this time, a cavity 28, which is surrounded by the pressing surfaces 21a, 25 and the cavity surface 26, is formed within the split-mold 20.
The male mold 21 is moved down while applying the pressure to the encapsulating resin 35 via the mold release sheet 30. Further, while applying the pressure to the encapsulating resin 35, the male mold 21 heats the encapsulating resin 35 so as to increase the temperature thereof to a value that can cause it to melt. Consequently, as shown in FIG. 3, the encapsulating resin 35 spreads out on the substrate 16.
When the male mold 21 contacts the second female mold 24, the mold release sheet 30 is clamped therebetween and is moved down together with them in the direction Z1. That is, the male mold 21 and the second female mold 24 are both moved down in the direction Z1.
The first female mold 23, on the other hand, is kept in a fixed state as shown in FIG. 4, and therefore a capacity of the cavity 28 is decreased while the male mold 21 and the second female mold 24 are both moved down. Thus, the encapsulating resin 35 within the cavity 28 is further pressed and thereby a resin layer is formed on the substrate 16.
With respect to the previously described manufacturing process, however, the pressing surface 21a of the male mold 21 is merely moved down and kept parallel with respect to the pressing surface 25 of the female mold 22. In other words, the male mold 21 is moved down toward the female mold 22 until a distance therebewteen approximately becomes equal to the height of a CSP type semiconductor to be manufactured. This downward movement applies a high molding pressure to the encapsulating resin 35 and causes it to spread out.
With respect to the process of forming the resin layer on the substrate 16, the molding pressure applied to a place (usually an approximately central portion of the substrate 16) where the encapsulating resin is placed is liable to become excessively high compared to that applied to a peripheral portion of the substrate. For this reason, the semiconductor chips formed on the central portion of the substrate 16 may be encapsulated in a higher molding pressure with the encapsulating resin 35. On the other hand, the semiconductor chips formed on the peripheral portion of the substrate 16 may be encapsulated in a lower molding pressure with encapsulating resin 35.
As a result, the conventional method for manufacturing the semiconductor device and the conventional split-mold used therein suffer from the following disadvantages.
One disadvantage in the conventional method is that the thus-formed resin layer may have no uniformity and for this reason the semiconductor chips after the substrate 16 is diced may vary in performance.
Another disadvantage in the conventional method is that, with the development of miniaturization and thinness of the semiconductor device, the semiconductor chips formed on the central portion may be damaged by an excessively high molding pressure, whereas the semiconductor chips formed on the peripheral portion may be incompletely encapsulated due to a lower molding pressure.
Still another disadvantage in the conventional split-mold 20 is that the mold release sheet 30 is attached to the male mold 21 by utilizing vacuum force that has limitations in holding the mold release sheet 30 and therefore it is possible that the mold release sheet 30 may be detached therefrom.
Still another disadvantage in the conventional split-mold 20 is that the mold release sheet 30 may generate wrinkles thereon due to deformation of the encapsulating resin. Such wrinkles must be certainly removed therefrom but this is difficult in the case of using only the vacuum force to suck the mold release sheet 30.
It is a general object of the present invention to provide a method of manufacturing a semiconductor device and a split-mold used in the method, in which the above disadvantages can be overcome.
Another and a more specific object of the present invention is to provide a method of manufacturing a semiconductor device and a split-mold used in the method, in which a resin layer can be formed using a uniform molding pressure and a mold release sheet used therein can be always kept in a tension state.
The above objects and other objects of the present invention are achieved by a method for manufacturing semiconductor devices, comprising the steps of preparing a split-mold including a first mold and a second mold, mounting a substrate, where a plurality of semiconductor chips are formed, on the first mold, forming a resin layer for encapsulating the substrate on the substrate such that a pressing surface of the first mold and a pressing surface of the second mold are brought close to each other so as to apply a molding pressure to the resin and make the resin spread out stepwise, and dicing the substrate into separate semiconductor device units.
The above objects and other objects of the present invention are achieved by a split-mold for manufacturing semiconductor devices by encapsulating a substrate, on which a plurality of semiconductor chips are formed, with resin. The split-mold comprises a first mold and a second mold, wherein the second mold is able to be moved relatively close to or away from a pressing surface of the first mold, and is provided with an inner portion and at least one outer movable portion that surrounds the inner portion and is able to be separately moved.
The above objects and other objects of the present invention are achieved by a split-mold for manufacturing semiconductor devices by encapsulating a substrate, on which a plurality of semiconductor chips are formed, with resin. The split-mold comprises a first mold and a second mold, wherein the second mold has a pressing surface that is provided with a mold release sheet, and the second mold has a mold-release-sheet mechanism holding a mold release sheet outside the pressing surface of the second mold and applying tension to the mold release sheet.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description of the invention and accompanying drawings which set forth an illustrative embodiment in which the principles of the invention are utilized.